The goal of this project is to understand the regulation of vaccinia virus post-replicative mRNA 3' end formation. In recent years it has become increasingly clear that post-initiation events in transcription, including transcription elongation, termination and RNA cleavage, comprise important control points for regulation of gene expression. Recent experiments demonstrate that post-replicative mRNA 3' end formation is regulated during vaccinia virus infection. [unreadable] [unreadable] The working hypothesis for this project is that several vaccinia viral gene products, including positive elongation factors (G2R, J3R), a transcript release factor (A18R), a site specific RNA cleavage factor, the RNA polymerase itself, additional associated factors (H5R, unidentified host factor), and at least one additional unidentified IBT resistance factor, work together, perhaps as part of a transcription elongation complex, to regulate formation of the 3' ends of intermediate and late vaccinia viral mRNAs. The aims of the project are designed to test, refine, and extend this hypothesis. Specifically, 1) an in vitro transcription assay will be refined and used to define the biochemical activities of several putative transcription elongation and/or termination factors, 2) new IBT resistant virus mutants will be mapped and characterized to identify novel transcription elongation factors and 3) a virus induced mRNA 3' end cleavage factor will be purified, and the protein and its encoding gene will be characterized. [unreadable] [unreadable] A study of regulation of post-initiation events in transcription is important for understanding regulation of vaccinia virus gene expression in particular, and the system may prove to be an important model for study of regulation of transcription elongation in eukaryotes in general. Importantly, the value this type of research in basic poxvirology to public health has been significantly increased recently given the potential for use of smallpox as a bioterrorist weapon. [unreadable] [unreadable] [unreadable]